The present invention relates to improvement in an optical image device which performs the conversion of an incoherent image to a coherent image, spatial frequency filtering, optical logic operations, etc. through utilization of photoconductivity and the electro-optic effect a crystal having a sillenite type crystal structure.
From the viewpoint of improving the resolution of the device, as described above, it is desirable to reduce the thickness of a single-crystal plate, but it is difficult to use the plate less than 100 .mu.m thick, because of a requirement of the physical strength necessary for the fabrication and handling of the device. Furthermore, it is desirable that the written image can be erased solely by voltage control, because this permits simplification of peripheral optical systems for applications of the devices, but the conventional device requires, for erasure, irradiation of uniform by blue light as well as voltage control.